std::deque

 

C++

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Technical Specifications

 

Containers library

array (C++11)

vector

deque

forward_list (C++11)

list

set

multiset

map

multimap

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

stack

queue

priority_queue

 

std::deque

Member functions

deque::deque

deque::~deque

deque::operator=

deque::assign

deque::get_allocator

Element access

deque::front

deque::back

Iterators

deque::begindeque::cbegin (C++11)

deque::enddeque::cend (C++11)

deque::rbegindeque::crbegin (C++11)

deque::renddeque::crend (C++11)

Capacity

deque::empty

deque::size

deque::max_size

deque::shrink_to_fit

Modifiers

deque::clear

deque::insert

deque::emplace

deque::erase

deque::push_front

deque::emplace_front

deque::pop_front

deque::push_back

deque::emplace_back

deque::pop_back

deque::resize

deque::swap

 

Defined in header <deque>
template<     class T,     class Allocator = std::allocator<T> > class deque;	(1)
namespace pmr {     template <class T>     using deque = std::deque<T, std::polymorphic_allocator<T>>; }	(2)	(since C++17)

std::deque (double-ended queue) is an indexed sequence container that allows fast insertion and deletion at both its beginning and its end. In addition, insertion and deletion at either end of a deque never invalidates pointers or references to the rest of the elements.

As opposed to std::vector, the elements of a deque are not stored contiguously: typical implementations use a sequence of individually allocated fixed-size arrays.

The storage of a deque is automatically expanded and contracted as needed. Expansion of a deque is cheaper than the expansion of a std::vector because it does not involve copying of the existing elements to a new memory location.

The complexity (efficiency) of common operations on deques is as follows:

• Random access - constant O(1)
• Insertion or removal of elements at the end or beginning - constant O(1)
• Insertion or removal of elements - linear O(n)

std::deque meets the requirements of Container, AllocatorAwareContainer, SequenceContainer and ReversibleContainer.

Template parameters

T	-	The type of the elements. T must meet the requirements of CopyAssignable and CopyConstructible. (until C++11) The requirements that are imposed on the elements depend on the actual operations performed on the container. Generally, it is required that element type is a complete type and meets the requirements of Erasable, but many member functions impose stricter requirements. (since C++11)
Allocator	-	An allocator that is used to acquire memory to store the elements. The type must meet the requirements of Allocator. The behavior is undefined if Allocator::value_type is not the same as T.

Iterator invalidation

There are still a few inaccuracies in this section, refer to individual member function pages for more detail

Operations	Invalidated
All read only operations, swap, std::swap	Never
shrink_to_fit, clear, insert, emplace, push_back, emplace_back	Always
erase	If erasing at beginning or end - only erased elements. Otherwise - all iterators are invalidated.
resize	Only if the new size is bigger than the old one.
pop_back, pop_front	Only to the element erased

Notes

• Under some circumstances, references are not invalidated by insert and emplace.
• push_back and emplace_back do not invalidate any references.

Member types

Member type	Definition
value_type	T
allocator_type	Allocator
size_type	Unsigned integral type (usually std::size_t)
difference_type	Signed integer type (usually std::ptrdiff_t)
reference	Allocator::reference (until C++11) value_type& (since C++11)
const_reference	Allocator::const_reference (until C++11) const value_type& (since C++11)
pointer	Allocator::pointer (until C++11) std::allocator_traits<Allocator>::pointer (since C++11)
const_pointer	Allocator::const_pointer (until C++11) std::allocator_traits<Allocator>::const_pointer (since C++11)
iterator	RandomAccessIterator
const_iterator	Constant random access iterator
reverse_iterator	std::reverse_iterator<iterator>
const_reverse_iterator	std::reverse_iterator<const_iterator>

Member functions

(constructor)	constructs the deque (public member function)
(destructor)	destructs the deque (public member function)
operator=	assigns values to the container (public member function)
assign	assigns values to the container (public member function)
get_allocator	returns the associated allocator (public member function)
Element access
at	access specified element with bounds checking (public member function)
operator[]	access specified element (public member function)
front	access the first element (public member function)
back	access the last element (public member function)
Iterators
begin cbegin	returns an iterator to the beginning (public member function)
end cend	returns an iterator to the end (public member function)
rbegin crbegin	returns a reverse iterator to the beginning (public member function)
rend crend	returns a reverse iterator to the end (public member function)
Capacity
empty	checks whether the container is empty (public member function)
size	returns the number of elements (public member function)
max_size	returns the maximum possible number of elements (public member function)
shrink_to_fit (C++11)	reduces memory usage by freeing unused memory (public member function)
Modifiers
clear	clears the contents (public member function)
insert	inserts elements (public member function)
emplace (C++11)	constructs element in-place (public member function)
erase	erases elements (public member function)
push_back	adds an element to the end (public member function)
emplace_back (C++11)	constructs an element in-place at the end (public member function)
pop_back	removes the last element (public member function)
push_front	inserts an element to the beginning (public member function)
emplace_front (C++11)	constructs an element in-place at the beginning (public member function)
pop_front	removes the first element (public member function)
resize	changes the number of elements stored (public member function)
swap	swaps the contents (public member function)

Non-member functions

operator==operator!=operator<operator<=operator>operator>=	lexicographically compares the values in the deque (function template)
std::swap(std::deque)	specializes the std::swap algorithm (function template)

Example

Run this code

#include <iostream>
#include <deque>
 
int main()
{
    // Create a deque containing integers
    std::deque<int> d = {7, 5, 16, 8};
 
    // Add an integer to the beginning and end of the deque
    d.push_front(13);
    d.push_back(25);
 
    // Iterate and print values of deque
    for(int n : d) {
        std::cout << n << '\n';
    }
}

Output:

13
7
5
16
8
25